1. Field of the Invention
This invention relates generally to interconnection of integrated circuits and, more particularly, to fabrication of circuit modules using prefabricated flexible interconnect layers.
2. Description of the Related Art
In one form of high density interconnect, an adhesive-coated polymer film overlay covers a plurality of integrated circuit chips in chip wells on an underlying substrate. A preferred method of laser-drilling vias in the polymer film is described in Eichelberger et al., U.S. Pat. No. 4,894,115, issued Jan. 16, 1990. The polymer film provides an insulated layer upon which is deposited a metallization pattern for interconnection of individual circuit chips through the vias. Methods for performing a HDI process using overlays are further described in Eichelberger et al., U.S. Pat. No. 4,783,695, issued Nov. 8, 1988, and in Eichelberger et al., U.S. Pat. No. 4,933,042, issued Jun. 12, 1990. Multiple layers of polymer overlays and metallization patterns are typically applied, and significant processing steps are required to complete these multilayer interconnects.
Prefabricated flexible interconnect layers having metallization patterns thereon are manufactured by companies such as Sheldahl Corp., Northfield, Minn. and Parlex Corp., Methuen, Mass., for example. Multichip module and other electronic assembly manufacturers conventionally couple integrated circuit chips and other components to the metallization patterns using mechanical assembly attaching techniques such as wire bonding, tape automated bonding, or solder bumps. A prefabricated flexible interconnect structure typically has at least one insulative film layer having a thickness sufficient to support metallization patterns on each side. The thickness is often between 1 to 5 mils (25 to 125 microns).
Jacobs, U.S. Pat. 5,055,907, issued Oct. 8, 1991, describes a method of forming a thin film multilayer wiring decal on a support substrate and aligning and attaching one or more integrated chips to the decal to fabricate a semiconductor substrate. Reach-through vias connect the decal wiring to the chips. The total thickness of the thin film multilayer decal is described as being on the order of 15 microns for four layers. Laser drilling vias that have bottom openings of 1 mil by 1 mil, for example, through polymers having thicknesses greater than two or three mils (50 to 75 microns) is possible, but can be more difficult than laser drilling vias through the thin layers described in Jacobs.